The invention relates to an antenna diversity system for the mobile reception of frequency-modulated signals comprising a receiver, antennae and a diversity processor. Such antenna diversity systems are preferably used for improving the radio reception in cars. Hitherto, mainly systems having two antennae have been employed. Such an antenna diversity system is known, for example, for European Patent Application No. 0 036 139 B1. In this case, the system is used for the stationary mode of reception. In this system, several reception signals are derived from the reception signals of two antennae with the use of phase shift devices and these signals are passed on to the receiver by means of a switch. With the use in cars, the dynamic behaviour of the diversity system is of major importance. Due to the movement of the car, the antenna voltages are varied constantly so that the signal quality has to be checked constantly. In contrast with the diversity system known from the aforementioned European Patent Application, the rapid identification of the occurrence of an interference in the reception signal is therefore absolutely necessary. The known system operates slowly because for a stationary use a given situation of reception exists for a long time. For the radio reception in the car, the transmission property of the path between the transmission antenna and the reception antenna is constantly varied during driving. The superimposition of electromagnetic waves having long different travelling times results in that an increased noise and a distortion of the low-frequency message are obtained at the output of the frequency demodulator. In the case of stereo transmission, this effect also leads to an increased cross-talk between the two stereo channels. Due to the movement of the car and due to the directional effect of the reception antenna, adjacent channel interferences and intermodulation interferences are varied. The system is often also disturbed by electrical interferences of the electrical aggregates forming part of the car.